The present invention relates to a process for preparing N-(.alpha.,.alpha.-dimethylphenyl)urea derivatives. More particularly, it relates to a process for preparing phenylisopropylurea derivatives by the addition of substituted ureas to isopropenyl aromatic compounds.
Phenylisopropylurea derivatives having the general formula: ##STR4## wherein Z is hydrogen, halogen, alkyl or haloalkyl; R' is hydrogen, alkyl, or alkoxy; and R" lower alkyl, substituted alkyl, alkoxy, phenyl or substituted phenyl are presently known and available compounds. The phenylisopropylurea derivatives are known to be potent herbicides, capable of supressing both sprouting of weed seeds and growth of weed seedlings.
These compounds can control such germinating grass weeds as crabgrass (Digitaria sp.), bluegrass (Poa sp.), foxtail (Alopecurus sp.), barnyard grass (Echinochloa sp.), or green foxtail (Setaria sp.), and such broadleaf weeds as lambsquaters (Chenopodium sp.), pigweed (Amaranthus sp.), or chickweed (Stellaria sp.). Especially these compounds are unique in that they exert their action against perennial weeds as nutsedge (Cyperus sp.), sedge (Carex sp.), or spikerus (Eleocharis sp.), which have previously been difficult to control.
The phenylisopropylurea derivatives generally exhibit very low phytotoxicity to such cultivated crop plants as peanuts, cotton and rice, rendering them especially useful and desirable for selectively controlling weeds in growing fields of these particular crops.
The phenyisopropylurea derivatives have been prepared by a variety of methods. In U.S. Pat. No. 3,972,909, for example, N-alkoxy- (or N-alkenyloxy)-N'-(.alpha.,.alpha.-dimethylbenzyl)-N-phenylureas, useful as selective herbicides, are prepared by reacting N-hydroxy-N'-(.alpha.,.alpha.-dimethylbenzyl)-N-phenylurea with a C.sub.1 -C.sub.4 haloalkyl or haloalkenyl compound, such as methyl iodide, in the presence of an acid acceptor such as sodium methoxide to form the N-alkoxy or N-alkenyloxy substituted N'-(.alpha.,.alpha.-dimethylbenzyl)-N-phenylurea in accordance with the equation: ##STR5##
In U.S. Pat. No. 4,039,577 another process for preparing a phenylisopropylurea derivative is disclosed which generally comprises reacting a cumyl halide of the formula: ##STR6## wherein X is halogen, with a urea or urea derivative of the formula: ##STR7## wherein R is hydrogen, phenyl, substituted phenyl, or phenyl alkyl, to form the phenylisopropylurea derivative ##STR8## wherein R is the same as defined above. It is also disclosed in said patent that because the cumyl halides are relatively unstable, they may be prepared in situ, by reacting, for example, .alpha.-methylstyrene with a hydrogen halide to form the cumyl halide and thereafter adding the urea or urea derivative, or the hydrogen halide may be added to a mixture of .alpha.-methylstyrene and the urea or urea derivative, whereby the cumyl halide formed in situ is reacted with the urea compound.
In U.S. Pat. No. 4,078,913, another method is described for preparing 3-(2-phenylisopropyl)urea derivatives which comprises reacting a phenylisopropyl amine compound, which has been prepared by reacting .alpha.-methylstyrene with thiocyanic acid to form a phenylisopropylthiocyanate which is further hydrolyzed to form the phenylisopropylamine, and thereafter reacting the amine with either a primary isocyanate compound or an amide chloride to form the 3-(2-phenylisopropyl)urea derivatives in accordance with the following equations: ##STR9## wherein Z is hydrogen or lower alkyl; R is hydrogen or alkyl; and R.sup.2 is lower alkyl, phenyl, substituted alkyl or substituted phenyl.
In U.S. Pat. No. 4,143,061 still another process for preparing 3-(.alpha.,.alpha.-dimethylphenyl)urea compounds of the general formula: ##STR10## wherein X is halogen or tifluoromethyl, n and m are 0 or 1, R.sup.1 is C.sub.1 -C.sub.2 alkyl or C.sub.1 -C.sub.2 alkoxy and R.sup.2 is C.sub.4 -C.sub.5 alkyl, cyclohexyl or phenyl, is disclosed which comprises reacting an isocyanate of the formula: ##STR11## with a secondary amine of the formula: ##STR12## wherein X, m, n, R.sup.1 and R.sup.2 are as described above.
Each of the above-described methods for preparing phenyisopropyl urea derivatives, although effective to provide useful herbicidal compounds, all require the handling and use of either harmful isocyanates or corrosive halo intermediates which is a serious disadvantage of each of the aforementioned methods.
It has now been discovered that useful herbicidal phenylisopropyl urea derivatives may be prepared without the use of isocyanates or halo intermediates by reacting an alkenyl aromatic compound and urea, or a substituted urea compound, in a polar aprotic solvent in the presence of certain acid catalysts.